Salinity acclimation modulates copper toxicity in the sheepshead minnow, Cyprinodon variegatus

The sheepshead minnow (Cyprinodon variegatus) is able to withstand a wide range of salinities. Salinity acclimation involves physiological and biochemical changes, which may influence how organisms respond to a stressor. The present study investigated effects of salinity acclimation on subsequent Cu toxicity. In experiment 1, fish were acclimated to a hyposmotic, isosmotic, or hyperosmotic salinity for 14 d and then exposed at these salinities to 16.6 µM Cu(2+) for 12 h. Survival differed during this Cu challenge; fish acclimated to 2.5 ppt salinity were much more sensitive to Cu than those acclimated to 10.5 or 18.5 ppt seawater. In experiment 2, fish were exposed to 14.6 µM Cu(2+) for 6 h after the 14-d salinity acclimation. Whole-body Cu, whole-body Na, liver lipid peroxidation (LPO), liver catalase activity, and liver glucose levels were determined before and after Cu exposure. Prior to Cu exposure, the acclimation groups differed only for liver glucose levels, which were higher in the 2.5 ppt acclimated fish than in the others. These same 2.5 ppt acclimated fish were markedly affected by Cu, having increased whole-body Cu and liver LPO and decreased whole-body Na levels. Copper exposure had generally insignificant effects for the 10.5 ppt and the 18.5 ppt acclimated fish. This study showed that even in euryhaline fish, salinity acclimation can have a drastic effect on Cu toxicity.